66 CRUSTACEA. 



Closely allied to the Copepoda are the Kpizoa, or 

 " fish-lice." This division of parasites contains a great 

 number of forms, which have been so entirely changed, 

 and often so degraded in structure, that it would not 

 be possible to recognize them as belonging to the class 

 if it were not, as in the barnacles, that the young are 

 in their early stages of development true Crustaceans 

 (Fig. 40). They are parasitic, living on or in other 

 animals, and specimens of some of them may be found 

 on fishes, attached to the gills, or hanging from the 

 skin just behind the fins, with the forward part of their 

 bodies deeply buried in the flesh. Having no need 

 of eyes, appendages, or of stomachs, as they take their 

 food directly by suction, or through the skin of the 

 body by absorption, they lose most of these organs, or 

 all of the more important ones, and become in some 

 cases mere sacks without shells or jointed appendages, 

 having no likeness to any normal articulated Crus- 

 tacean. Lemea branchialis (Fig. 40) is one of the 

 most degraded forms of this order, and is not un- 

 common on the gills of codfishes. Its body is not 

 segmented, and ends in two long egg-masses. It is 

 destitute of locomotive appendages and sense-organs. 

 The parts around the mouth are modified into root-like 

 appendages, and these are buried in the flesh of the 

 animal upon which this parasite feeds. 



The curious extent to which parasitic habits may 

 alter the organization can be studied in the very 

 familiar animal, the little Oyster crab (Fig. 30, p. 62), 

 which can be obtained from oyster-openers by the 

 hundred, if wanted. In this case a Decapod, or true 

 hard-shelled crab, living inside of the oyster and brows- 



